Summary

Made a thicker roller so that the spool is more centered, allowing it to roll smoother. The 40mm can be used with most spools. Pictured is an Esun spool.

The 36mm is used for the Esun spool adapter for refilament (https://www.thingiverse.com/thing:5691798) as it has a smaller hole.

It fits a 608ZZ bearing, in case you're gonna be using this other than the KP3S Top Mount Spool Holder (https://www.thingiverse.com/thing:4600120)